Sewage treatment



Sept. 6, 1938.

A. J. FISCHER SEWAGE TREATMENT Filed Feb. 28, 1935 LIME flun'fwn FIG. I /4 i a i] f d M INVENTOR.

ANTHONY J. FISCHER ATTORNEY.

45 sludge, and all of Patented Sept. 6,1938

N. Y., assignor to The Dorr Company,

Inc., New

York, N. Y., a corporation of Delaware Application February 28, 1935, Serial No. 8,584

3 Claims.

The present invention relates to the treatment of sewage and analogous organic wastes.

Heretofore, in the purifying of sewage by steps involving sedimentation for obtaining on the one 5 hand a resulting efiluent sufliciently clear to deliver to streams or other places for suitable disposition thereof, and on the other obtaining from the sedimentation of organic solids a disposable sewage sludge, there has been attempted the employing of coagulants or precipitating agents. In certain processes as heretofore attempted, certain disadvantages have been experienced because of the colloidal and slimy nature of the resulting sewage sludge, and which were of a character that necessitated specific modes of handling the sludge, particularly incident to the disposing thereof. In fact, according to certain of the prior modes of sewage disposition, where coagulating reagents have been used, it has been customary to handle the sludge by a process involving the dewatering of the same by spreading it over drying beds. Even with this type of disposition, certaln troubles are experienced because of the nature of the sludge. In certain other processes heretofore attempted primary and sec-' ondary sedimentation have been employed'with chemical dosing between the sedimentation steps and'the resulting sludges subjected to digestion. In that instance where acid reagents were used the resulting mixed sludges tended toward predominating acid characteristics and on the contrary where alkaline reagents were used the resulting mixed sludges tended toward predomihating alkaline characteristics. Extremes of 3 eitherof these characteristics are detrimental to digestion and the present invention has in view the producing of sludge more readily responsive to bacteriological digestion.

According to the present invention multi'-stage chemical dosing and a multi-stage sedimentation are employed with a consequent collecting or disposal of the sludge from each sedimentation stage, according to steps involving the ultimate digesting of. the solids content of the sewage this without the experiencing of difliculties such as those above referredto.

According to certain modes, of realizing the invention, raw sewage is subjected to a lime dosing-sometimes referred to as liming"-and which involves adding and mixing a reagent to supply the requisite lime or analogous alkaline reacting constituent, whereby there is provided for the incoming sewage that chemical reagent which aids or furthers the chemical coagulation and precipitation of the solids, and which also (on. any-2) flocculation operation between this primary alka- 5 line dosing and the primary sedimentation. A According to the second chemical dosing and second sedimentation stage, a chemical reagent is supplied to and mixed with the eflluent'from the primary sedimentation, as for example, alum, 1o ferric chloride or chlorinated ferrous sulfate (chlorinated copperas), of a character to cause flocculation and to aid ultimate chemical precipitation of the solids content that still exists in the effluent from, and thus escapes from, the 15 primary sedimentation. This second chemical treatment is properly referred to as a second chemical dosing and is of a character to neutralize or diminish the alkalinity in the eifiuent or to substantially do so. This second closing is m preferably followed by aperiod for allowing fioc to develop and after this flocculation period the eilluent is subjected to secondary sedimentation, with the result that a chlorinated and relatively sterile eflluent passes from the secondary sedig5 mentation, and with the result that a sedimented sludge is derivable from the secondary sedimen tation which is relatively neutral or at the most has only slightly acid or alkaline characteristics. The sludge from this secondary sedimentation 3 being relatively neutral or only slightly acid or alkaline is employed to modify the' alkalinity experienced in connection with the settled solids derivable from the sedimentation of the limeddosed sewage as carried out in the primary sedimentation .zone. This modifying of the-highly alkaline solids by the mixing or inter-mixing therewith of the relatively neutral or only slightly acid or alkaline solids derivable from the secondary sedimentation maybe accomplished by 40 effecting the mixing of the sludge from the primary sedimentation with the sludge from the secondary sedimentation at a location-for ex-- ample in a digester--which is outside of either the primary or secondary sedimentation, while according to another form or mode of realizing this feature of the invention, the sludge from the secondary sedimentationmay be passed to I an earlier portion of theprocess, whereby it will be subject to a sedimentation in the primary sedimentation basin, together with the other solids initially precipitated following the lime dosing of the incoming sewage.

Patentable aspects of the invention revolve about the features above referred to, which characteristically typify the essence of the present intively alkaline condition to the raw sewage or, vention and the novelty thereof'over the prior to the ewage sludge or sediment obtainable as attempted practices. a a result of said primary sedimentation, provided The novel features that are considered charnothing else is added to overcome or lessen the 5 acteristic-of this invention are set forth with paralkaline characteristic, an eifect which is partic- 5 ticularity in the appended claims. The invenularly realized by the operation as carried out in tlon itself, however, both as to its organization Fig. 1'. and mode of operation, together with objects and The supernatant within the primary clarifler advantages thereof,'will best-be understood from passes as eiliuent therefrom along the path I and the following description of the speciflc embodi-' a second dosing is efl'ected by the supplying of 10 ments when read in connection with the accoma chemical acid reagent to the eilluent and the panying drawing forming a part of this speciflcaeifecting of a substantial and intimate mixing of tion. Y a the thus added chemical by the secondary mix- In' said drawing each figure thereof illustrates, ing or agitator means 8. The chemical or acidua system or arrangement having apparatus prolating. agent added at this point is of an acid 15 viding for multi-stage chemical dosing and multicharacter that substantially decreases or neuy' 'stage sedimentation of sewage sludge, and also tralizes and thus modifies the alkalinity of the employ a digester, wherein the solids content eflluent. In other words, the acid chemical thus of the sewage as derived from the sewage sludges added is suflicient to cause the eilluent to be left obtained from primary and secondary sedimentaneutral or only slightly acid or alkalized. This 20 tion zones are subjected to anaerobic biologic chemical is also of a character to aid or encourdig'estlon with the consequent production of a age flocculation and therefore there has been combustible gas. provided a further flocculation zone 9 that re- Inli'ig. 1, an arrangementis shown in which ceives the dosed eflluent flowing thereto from the there is arranged in series a mixing apparatus mixer 8. The eiiluen flow has a slow movement 25 into which chemically dosed raw sewage is fed through the flocculation zone whence it is prefand mixed, from which the dosed, mixed sewage erably subjected to slow agitative movement propasses to a flocculation acne, thence to a primary duped, such as by paddles within, under condiclarifler providing an initial sedimentation basin tions to facilitate flocculation. Therei'rom the soior zone from which the eilluent passes, is closed 'eiliuent with the flocs formed the ein passes along and then passes to a mixer, thence-to another 1 the path ll into the secondary clarifler or sediflocculation zone and ultimately to a secondary 'mentation basinl I. In this secondary sedimenclariiier providing a secondary sedimentation tation basin thesewage liquid therein is retained basin or zone, and from the latter of which the for a sufficient time to cfl'ect a substantial sedi- 5 clarifled eiiiuent passes to the river or to other mentation of'the. solids remaining therein with place of disposal. According to the arrangement the result that the supernatant thereof passes of this ,figure, sludge derivedfrom the primary therefromas a relatively clarified eiliuent along sedimentation and sludge derived from the secthe path l2 ondary sedimentation is passed to a digester and I The sewage sludge derivable from-the primary 0 these sludges'are either mixed ahead of the diclarifler in the form of an alkaline sludge is with- 40 gester. or in the digester. drawn from the primary clarifler and passes According to 2 there is an arrangement of therefrom along the path it to "the digester l4, i i x 111111181 fl l ion Z 11 Initial lflrwherein anaerobic biologic digestion of the sludge fl $800111!!! mixer, eco u t on is carried out, or inother'words wherein a dizone and secondary clarifler practically after the gestionatreatment is carried out that is eifective v r' order of Fig.1, but in the arrangement of Fig. 2, upon the sludge or sludges therein/while in a the sludge derivable as a result 01 the p im y state of liquid consistency during the course of r r P m y im ntation s p ted dldigestion treatment. The sludge or sediment rel t0 h mflterludge iv le from th sulting from the-secondary sedimentation is colsecondary I entation-is passed back. and inlected and withdrawn from the secondary claritroduced into the incoming sewage stream, either fler or sedimentation basin II and passes thereahead of the initial mixer, initial flocculation zone from along the path Ii, by which it is delivered or initial clarifier. g 1 at it into the sewage sludge flowing from the l tefer nce 18 now de tothe dra ng in prlmary clarifler to the digester along the path I ",providing the valve at 'l'| is open. As an The incomingsewageis supplied along the path alternative, the sewage sludge from the second- I, and lime or other alkaline dosing reagent is ary clariiier can be passed along the path ii supplied thereto at the point 2. Thethus dosed and be delivered at ll, provided the valve at i9-- n mi g sewa n ers th mix r or a itator}, is open, directly to the digester wherein it is wherein an' intimate or relatively thorough mixintimately i ed with and the. sludge supplied 8 the ing ma ial with the incoming-A .to the digester-alon'g the path ,thus providing 3 sewage is insured or efl'ected, and therefrom the within the digester a sludge mixture wherein the incoming sewage to. which the alkaline reagent solids thereof undergo con-current digestion. has-thus been supplied and intimately mixed If some or all of the sludge can be a pm as longtime path [into t primary fl passed from the secondary sedimentation basin, 5 culation zone I, thence-to and into primary nalong the path It for introduction into the in- .iier 6. wherein the primary sedimentation is car- Coming to h D ma y initi ried out sothat there isrealized a substantial m t flni d e thus P se m the e tling of the organic solid content of the sewsecondary sedimentation-into the incoming sew- 10 age. This settling is aided or furthered as a reage may be referred to :as return sludge and may 79 suit of the chemical treatment which e'fbe' introduced into the incoming sewage under i'ects a coagulation or precipitation of the orconditions whereby it is mixed with the latter tonie s id o t in the sewa edosing gether with lime supplied as along the line 2 and by lime or other suitablealkallzing material is with antiseptic chlorlnes supplied asalong line 7; also sufficient to insure the imparting, of a rela- 2|. 4 Such antiseptic chlorines will have 'a sterilnuclei initiated or yielded in Fig. 1, and therefore eiliuents as delivered from the primary sedimentation and as delivered from the secondary sedimentation.

The fiocculating zones or apparatus indicated at 5 and 9 are for obtaining generally the effects of the teachings of the Smith Patent No. 1,893,451 of January 3, 1933, namely, that floc by chemical or other action, are conditioned as the liquid bearing them passes or drifts through the flocculating zone which is equipped with current-producing de-' vices, characterized by a plurality of paddle-like assemblies, including blades moving in repetitive paths, which in the embodiment illustrated have By virtue of the the paddlesubstantially horizontal axes. gentle agitative eifects produced by like assemblies, bidity in the liquid are amassed, coagmented or developed into integrated flocs that have been conditioned into settleability.

The sedimentation zones, or settlers, 6 and II v are preferably what is known as clariflers that are continually operating tanks provided with an overflow launder; for efliuent, and a travelling sediment-raking or scraping mechanism for discharging sludge from the tanks.

The mixers 3 and 8 are preferably rapid-mixing or agitator devices that are well known.

The chemicals usable for alkalizing the sewage or polluted liquid are lime or other alkaline material, while the acid reacting or acidulatingchemicals should produce ultimately an environment that has no substantial toxic effect 'upon the organisms in the biologic digester l4. Preferably they should be the chlorides or sulphates of iron, aluminum or zinc, or possibly mixtures thereof. v

The digester I4 is preferably of some knowntype wherein anaerobic bacterial orjbiologic conversion or digestion takes place for the rendering inert and innocuous of putrescible and' other organics of the sewage sludge.

The arrangement of Fig. 2 comprises an initial mixer 3, an initial flocculation zone 5', an initial' or primary clarifier or sedimentation basin 6', a secondary mixer 8, a secondary flocculation zone 8 and a secondary clarifier or secondary sedimentation basin ll having embodiments of the same arrangement like numbers havebeen accorded to the like parts of both Figs. 1 and 2. In the arrangement of Fig. 2 there is indicated a chlorine supply at 2i, whereby the limed or alkaline dosed incoming sewage can to a certain extent be chlorinated, thus rendering sterile to a certain extent the incoming sewage. Also according to this Fig. 2 the secondary clarifler is shown as having a connection whereby the sewage sludge derived as a result of the secondary sedimentation can be introduced into the incoming sewage as at any of the points 22', 23 or. 24, according to which of the respective valves 25, 26 or 21 is open. Thus it will be seenthat the initial mixer can be relied upon to effect -an intimate mixing of all materials or substances introduced into the sewage ahead of the initial mixer 3, such as lime or other alkaline dosing or coagulating material or sewage sludge derived from the secondary sedimentation and which is passed back to the incoming sewage, rine supplied at 2|. In the primary clarifler, a

sedimentation-oi the-incoming sewage thus sup--- plied takes place and it passed back secondary sludge can be relied upon the flocs and particles of turas that shown and 33,- assuming valve or the chic; I I can be passed, either to the treating system,-

sludge from the secondary basin II or any part will be noted that the of a chemical reagent having a strong acid radical, to wit, chlorinated ferroussulfate or chlorinated. copperas, which ingredients result from the prior chemically combining of Cland FeSO; as a chemically reactive product into the-clarifled eiliuent leaving the primary clarifier but prior to the introduction of said clarified efliuent into the secondary mixer. The chlorine component thus supplied by the chlorinated copperas is relied otherwise be imparted asis also indicated the introduction or application upon for rendering still more sterile the liquid component of the effluent and whereby this sterile condition exists not only in the supernatant liquid in .thesecondary clarifier but also in the effluent leaving the secondary clarifier and which is provided by the supernatant liquidtherein.

The copperas is added prior to the mixing in order to aid in the ultimate flocculation which'is carried out in the flocculation zone 9 and thus ultimately aiding in the throwing down as a result of the sedimentation the solids content r'e maining in the effiuent. I

i In the arrangement of this Fig. 2 it will be ncted that the only sludge thus far described as supplied to the digester I4 is that which is supplied thereto from the primary clarifie'r along the path 28, this is because the sludge from the primary clarifier not only contains the solids deposited for the first time'therein, but it also has intermixed solids introduced into the incoming sewage as the result of the passing back into the incoming sewage of sewage sludge derived asthe result of the said secondary sedimentation. It is therefore apparent that the sludge derived as the result of the primary clarification in this arrangement also. includes some solids which have been passed back into the incoming sewage and which have been reprecipitated in the primary or initial clarifier.

' It will be manifest also that the arrangement and steps described in Figs. 1 and 2, can be modithe invention, as for example it would be possible to pass some of the sludge derived from the' secondary sedimentation directly to the digester and to pass other portions of the sludge derived from the secondary sedimentation into the incoming sewage at a clarifler, as for example by passing some portion of the sludge from the line I5 along'paths 29 at 30 is open, and by passing other portions of the sludge along line 22, assuming valve 25 is open.

The design may have eflluent discharge means indicated at M and digested sludge discharge means indicated at 32.

From the foregoing description relating to the arrangement of this Figure 2, it will be manifest that according. to the will of an operator the sludge from the secondary sedimentation basin all thereof or only 'a part thereof, along the path l5, SI .and 22 to the line I along which incoming sewage passes on its way or if desired, all .of the point ahead of the primary fied and still be within the scope and purview of to and into digester If.

It'is to be noted that while lime or other alkaline or alkalizing reagents may be used in the initial coagulation bining a of the two chemically dissimilar coagulating steps as herein'outlined efl'ect the ultimate desired clarification with a relatively small amount of or a lesser cost for chemicahneagents. The separation of the application of these chemi- The diagrams of the clearly indicate the flexibility of the process and alkaline sludge said thus derived sludges, and treating themingled-sludges by anaerobic biologiedigestion.

2; The method oi'treating sewage and'the likefi and the'digesting of sludge therefrom, which 1 anaerobic biologic gether, with the description hereby presented,

4 a 9,189,867 thereof can be passed along the path 20 and it therefrom alkaline characteristics, subjecting the alkalized sewage to primary sedimentation, separately withdrawing as a result of said sedimenta-. tion an alkaline sludge and. supernatant eiiluent liquid, mixing with said having a strong acid radical to impart tothe sludge derived therefrom preferably neutral but at most only slightly acid characteristics, flowing said mixture through a flocculation 'zone equipped with current-producing devices characterized by a plurality of p'addlelike assemblies including blades mo'ving in repetitive paths for yielding from said mixture coagmented and amassed flocs conditioned into efliuent an acidulating agent reactable therewith settleability, subjecting flocculated liquid therei from to secondary sedimentation, wlthdrawing'as a separately result of said secondary sedi- 3. The method-of treating sewage and the like, 

